The present invention relates to an ion trap, a reaction or fragmentation device, a mass spectrometer, a method of mass spectrometry, a toroidal ion trap and a method of trapping ions.
U.S. Pat. No. 6,872,938 and U.S. Pat. No. 7,425,699 each disclose a method of introducing ions into an electrostatic ion trap or mass analyser. A storage device is provided comprising a curved RF confined rod set known as a C-trap in which ions are trapped by application of trapping voltages at the entrance and exit ends. However, the C-trap suffers from the problem of having a limited trapping capacity due to space charge effects. This restricts the performance of the downstream electrostatic ion trap or mass analyser.
WO 2013/027054 discloses, in relation to FIGS. 11A and 11B, an ion trap mass analyser that traps ions in a toroidal DC potential well. Ions are mass selectively ejected from the device in a radial direction. More specifically, an excitation field is applied to the device so as to excite ions of a particular mass to charge ratio out of the DC potential well and radially inwards towards the centre of the device. The excitation field is then varied so as to mass selectively eject ions of a different mass to charge ratio. However, as the device is specifically configured to mass selectively eject ions of a specific mass to charge ratio at any given time, the device is unable to simultaneously eject a large ion population of ions having a range of mass to charge ratios. The device is therefore unable fully exploit the large trapping volume that the toroidal trapping region provides, because the large ion population cannot be ejected simultaneously. Furthermore, as the ions must be excited out of the DC potential well in order to be ejected from the ion trap, this may complicate the downstream trapping or processing of the ions ejected from the trap.
Daniel E. Austin et al. “Halo Ion Trap Mass Spectrometer”, Analytical Chemistry, vol. 79, no. 7, 1 Apr. 2007, pages 2927-2932 also discloses a toroidal ion trap mass analyser from which ions are mass selectively ejected in a radial direction. A toroidal trapping field is arranged in the device by applying different RF voltages to the electrodes (see introduction; and page 2929, right column, first paragraph). An RF excitation field is applied to the device so as to mass selectively eject the ions out of the toroidal trapping field and towards a detector (see page 2929, right column, first paragraph; and the paragraph spanning the two columns on page 2931). Accordingly, this device suffers from the same problems as those described above with respect to WO 2013/027054. Additionally, the device is complicated by the use of RF voltages to form both the toroidal trapping region and also the ejection field.
It is therefore desired to provide an improved ion trap, spectrometer and method of spectrometry.